The use of timing signals in electronic apparatus is well known. Such timing signals have heretofore been commonly derived from one or more timing signal generators such as a master clock that provided an output train of clock pulse to the electronic apparatus for timing purposes.
Where an electronic apparatus is dependent upon receiving timing, or a plurality of clock pulses from a master clock, such apparatus can often be damaged if the master clock, or one or more derivatives thereof, should fail. This is particularly true where a microprocessor, programmed logic array (PLA), or other form of clocked digital logic circuits are in a control or other sensitive environment. For example, where a master clock system is utilized to control a motor driven digital, or magnetic data, recording device, and where clock pulses may also generate recording signal timing, the clocked motor control and/or motion validity checking could become unstable and cause apparatus damage and/or information loss if the master clock or one or more derivatives of the master clock should fail.
Systems and methods have heretofore been suggested and/or developed for sensing clock failure. General examples of such systems and methods may be found, for example, in U.S. Pat. Nos. 3,496,477 and 3,458,822.
In addition, systems and methods have been heretofore suggested and/or utilized for sensing different characteristics of a plurality of pulses in a pulse train, such as, for example, failure of one or more of the pulses in the pulse train and/or detection of gaps or the like in the pulse train. In this respect, see, for example, U.S. Pat. Nos. 3,068,367; 3,399,351; 3,800,234; and 3,903,474. In addition, detection of pulse failure within a pulse train after a predetermined time interval utilizing resetable counters has heretofore been suggested (see U.S. Pat. No. 3,350,580), and systems have heretofore been suggested for detecting failure of either one of a pair of timing generators including detection where an output signal from either generator is stuck and does not transition (see, for example, U.S. Pat. No. 3,795,867).
A monitoring system and method has still been needed, however, that is capable of monitoring a plurality of electrical conductors to assure the occurrence of transitions of the signals on each of the conductors, and particularly to assure monitoring of clock signals on a plurality of electrical conductors to assure transitions of each clock signal adjacent to the point of distribution to a controlled apparatus, and furthermore having the clock signals timed by a plurality of asynchronous timing pulses.